PoS(ICRC2015)1044 http://pos.sissa.it/ level. During level. σ σ 1 . 4 . neutrino fluxes were performed level. µ ¯ ν σ + 2 . µ ν and e ¯ ν + . Measurements were made of the strength of the e σ ν 5 > ∗ In particular, the energy spectra in the sub-GeV to TeV range was measured and compared The azimuthal analysis measured the east-to-west asymmetry in the neutrino flux, caused by A search for a long-term correlation between the atmospheric neutrino flux and the solar mag- [email protected] [email protected] [email protected] Speaker. Three direct measurements of the atmospheric effect as functions of energy andthe zenith asymmetry angle. was There dependent was on also zenith an angle, indication seen that at the the alignment 2 of netic activity cycle was performed, howevercalculated the to expected be effect relatively based small. on An the indication of HKKM a model correlation was was seen at the 1 using the Super-Kamiokande water Cherenkov detector:tra, the the directionally-integrated azimuthal energy spec- spectra, and the modulation of the fluxes with timeto over the the 11-year predictions solar cycle. ofinconsistent various with the published data, flux some preference models. wasmodel. seen for While the HKKM11 none model of as the the most realistic models werethe strongly geomagnetic field, for both flavours at particularly strong solar activity events, known asavailable, Forbrush but decreases, a no deviation theoretical from prediction the is expected neutrino event rate is seen at the 2 ∗ Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. c

The Super-Kamiokande Collaboration Kimihiro Okumura Institute for Cosmic Ray Research, theE-mail: University of Tokyo Takaaki Kajita Institute for Cosmic Ray Research, theE-mail: University of Tokyo Euan Richard Measurements of the Atmospheric Neutrino FluxSuper-Kamiokande at Institute for Cosmic Ray Research, theE-mail: University of Tokyo The 34th International Cosmic Ray Conference 30 July- 6 August, 2015 The Hague, The Netherlands PoS(ICRC2015)1044 Euan Richard (MeV) but so far 000 km away from O , 13 ∼ 2 (PeV), and atmospheric neutrinos can be detected up to O Atmospheric neutrinos are generated from the decay of mesons produced in cosmic-ray in- The atmospheric neutrino sample spans a wide energy region, peaking at Current atmospheric neutrino flux predictions are given by Monte Carlo simulations by several The estimated uncertainties on the simulations, especially at lower energies, were historically teractions in the Earth’ssources. atmosphere, and Since are the one first1960s of detection [1, of the 2], further the main measurements atmospheric experimentally offinite neutrino them available in neutrino brought neutrino the underground masses) discovery experiments of in in neutrinohas 1998 the oscillation improved (and [3]. quickly, thus by Since usingtor then [7, the 8, the atmospheric 9, understanding [4] 10], and of data accelerator the in [11, combination oscillation 12, 13, with parameters 14] solar sourced neutrinos. [5, 6], reac- groups, such as the HKKMdata [16], such Fluka [17], as and the Bartolatmosphere primary [18] by cosmic models. particle ray These detectors proton models onaccelerator are flux balloons experiments. based and and Direct on the spacecraft, experimental secondary and measurementsby of hadron muon the the production flux, flux Frejus measured measured energy in [19] spectra inthe were collaboration the made AMANDA-II (before [20, neutrino 21] oscillation and100 was TeV IceCube range). known), [22, and 23, more 24] recently collaborations by at higher energies (up tomuch smaller the than the uncertainties on theas direct the experimental current measurements of generation the of flux.atic neutrino However, uncertainties, detection measuring experiments the improve atmospheric statisticsincreasingly neutrino and useful flux reduce – by system- allowing direct more accurate dataof cross-checks measurements the and becomes simulations, feedback and to discovery the of future severalbut new development not effects that yet have observed, been such predicted asthesis by the directional presents simulations asymmetries three and direct modulation measurements(SK): over of the time. the directionally-integrated Specifically energy atmospheric this spectrum neutrino ofto flux the 10 at TeV flux range), Super-Kamiokande (with the azimuthal high spectrum, statisticsyear and in solar the the modulation cycle. 100 of MeV the flux with time over the eleven- Measurements of the Atmospheric Neutrino Flux at Super-Kamiokande 1. Introduction measured up to their initial creation point (i.e.source as after a crossing varied thesample, and diameter an accurate high-statistics of prediction of the neutrino the Earth). expected beam, fluxand depending however They on time to neutrino are is flavour, energy, understand direction, thus required. and atheir use useful For expected them example, zenith as the angleatmospheric a discovery distribution neutrino of with is neutrino not and just oscillation without asuch was signal as oscillation by but astrophysical applied. also comparison neutrino, a proton of backgroundthe decay, Furthermore, source flux and the is to dark thus many matter of other searches. paramount experiments, the importance An planned to accurate Hyper-Kamiokande many prediction current [15] of and experiment future couldneutrino experiments. use mass As the hierarchy. one atmospheric example, sample to uncover the PoS(ICRC2015)1044 µ µ ¯ ν ν 2 MC -like (2.2) (2.1) + . Our χ µ 1 µ and ν e ν and Euan Richard , where e ¯ ν -like and e of the + 2 MC e 2 χ ν χ flux. The strength of − µ ν is with respect to a flat 2 flat as χ 2 flat A in the fitting q χ B . The plots used to determine this σ 5 2 > k west west n n ) + B − + 3 + φ east east ( is the azimuthal angle. This parameter as a function n n . sin φ 4 = 1 k A . A numerical comparison was performed by calculating the level, by using the parameter 2 σ 2 , and the significance was taken as . 5 , from which we define the parameter 3 induced sample. µ ) represents the number of east-going (west-going) single-ring events in the SK ν are free parameters, and . Our measurement gives the discovery of the effect for the or 2 e A west k ν / n ( A ∆ statistic with respect to the HKKM11 MC prediction and and 1 2 . This parameter is simply a measure of the dipole asymmetry strength; the significance is east 1 k n χ Which is a sample whereby a single electron-like or muon-like track is reconstructed inside the detector, and is a Furthermore, an indication of a predicted shift of the dipole asymmetry angle depending on The azimuthal spectra showed an east-to-west dipole asymmetry in the neutrino flux, caused Measurements of the atmospheric neutrino flux were performed using the water-Cherenkov The energy spectra were measured in the range 100 MeV up to 10 TeV, as shown in Fig. 1 statistic, taking into account the error correlation matrix. The combined 2 χ where of zenith angle is shown in Fig. events simultaneously. This isfield the effects on first the attempt neutrino flux at beyondmeasurements a a give simple measurement confidence east-west that asymmetry. that the Altogether, explores these fluxthe azimuthal the simulations geomagnetic correctly geomagnetic field. model the complicated effects of distribution (i.e. assuming no zenith dependence of the dipole angle), considering dataset defined as very high purity where this dipole asymmetry was furthermore shown toby depend on the neutrino HKKM11 energy model, and as zenith as shown predicted in Fig. is the the zenith angle was seen at the 2 by the geomagnetic field, for both neutrino flavours at measured data provided significantly improved320 precision MeV. We up compared our to results 100 GeV, againstmodels, and the as the predictions shown graphically first from in several data Fig. atmospheric below neutrino flux fluxes (corresponding to 23 bins)and was Bartol found models to respectively. be Westrongly see 21.8, that inconsistent 25.6, while and with none 30.7 our of forbest-fit the data, to the current there our HKKM11, generation data. was Fluka, flux models Energy someantineutrino are spectra enriched preference measurements samples, for were which also also the showed obtained HKKM11 agreement using with model separate the neutrino as current and flux the models. significance are shown in Fig. detector Super-Kamiokande [25], whichinteractions, has with the an world’s exposure of largest approximately dataset 315 kton of yr. atmospheric The atmospheric neutrino Measurements of the Atmospheric Neutrino Flux at Super-Kamiokande 2. Measurement and Results fluxes were measured and analyseddetailed as analysis a of function systematic of errors. energy, azimuthal direction, and time, with a PoS(ICRC2015)1044 . 6 Euan Richard 5 /GeV) fluxes at SK, shown ν µ ¯ ν (E + 10 µ 4 ν Log and e ¯ ν + 3 e ν level. This correlation is shown in Fig. 2 4 σ level. 1 . σ e µ 4 ν ν . unfolding forward folding µ µ ν ν 1 unfolding forward folding e µ µ ν ν ν e µ ν ν Super-Kamiokande Super-Kamiokande Frejus Frejus IceCube IceCube IceCube AMANDA-II AMANDA-II 0

-1

-1 -3 -4 -5 -6 -7 -8 -9 -2

10 ν 10 10 10 10 10 10 10 10

Φ [GeV cm [GeV E ] sr sec

-1 -1 2 -2 The measured energy spectra of the atmospheric By separate examination of several short periods (not included in the long-term analysis due These direct measurements of the atmospheric neutrino flux tested the theoretical models with A study of the time correlation between the atmospheric neutrino flux and the solar magnetic to lack of a theoreticalthe SK prediction) operational corresponding period to for especiallyatmospheric a neutrino strong total flux solar exposure was of activity, seen 7.1 at from the days, across 2 an indication for some decrease in the improved precision, and searched for several new physical effects not previously measured. While 3. Summary and Future Figure 1: Measurements of the Atmospheric Neutrino Flux at Super-Kamiokande activity cycle was performed, where the solar activityflux was at assumed ground to level. be correlated The with type theHKKM of neutron correlation group between was the calculated neutrino and todata, neutron have flux but a predicted by relatively by searching minor the over effect twoerence on for solar most such maxima of a using the correlation approximately was Super-Kamiokande 14 seen years at of the data, 1 a slight pref- in comparison to measurementsHKKM11 by [16] model Frejus predictions are [19], alsolines. AMANDA-II shown in [20, solid 21], (with oscillation) and and dashed IceCube (without [22, oscillation) 24, 23]. The PoS(ICRC2015)1044 Euan Richard 4 360 GeV) 300

/

3.5 (E fluxes at SK, divided by the 240 10 Azimuth [deg] µ ¯ 3 ν 6. + Log . 180 µ 0 ν < 2.5 ) 120 and e ¯ ν 2 60 zenith + ( e μ-like ν cos 0 1.5 < 850 800 750 700 650 600 550 500 6 5 . 0 -like neutrino induced events in the SK-I to SK-IV data discovery level, even those with relatively low sig- 1 − Bartol Fluka µ σ 360 0.5 300 -like and e 0 240 Azimuth [deg] HKKM11 HKKM07 µ e ν ν 180 -0.5 120 -1 0 GeV and incoming angle 1 1 .

3 1.4 1.2 0.8 0.6 0.4 0.2 1.4 1.2 0.8 0.6 0.4 0.2 1.8 1.6 1.8 1.6

60

Ratio Ratio < e-like rec 0 E 700 650 600 550 500 450 400 350 < A subset of the single-ring The measured energy spectra of the atmospheric 4 . In future, combining our measurements with those from other current generation neutrino de- Figure 3: (points) and MC (boxes), optimized toenergy show 0 the east-west asymmetry by selecting events with reconstructed Figure 2: Measurements of the Atmospheric Neutrino Flux at Super-Kamiokande predictions from the HKKM11 fluxare model. also The shown. ratios of several other flux models to the HKKM11 model tectors, which are sensitivemay at be distinct obtained. but For overlapping example,measurement energy constraints combined given regions, with by even other the more measurements improved precision at accurate of higher data our energies energy can spectra help to accurately deter- nificance are interesting indications thatdetectors. suggest further Our study measurements by arewhich the gives in next confidence general in generation our consistent of understanding with neutrino and the modeling of current the generation atmospheric neutrino flux flux. models, only one new measurement reached the 5 PoS(ICRC2015)1044 1 ) 1 ) Euan Richard zenith 0.8 0.8 zenith cos( 0.6 0.6 e-like cos( μ-like 0.4 0.4 0.2 0.2 -like neutrino induced events -like neutrino induced events 0 0 µ µ -0.2 -0.2 -0.4 -0.4 -like and -like and e e -0.6 -0.6 -0.8 -0.8 μ-like -1 -1 0 0 0 0.1 0.1 80 60 40 20 0.08 0.08 -20 -40 -60 -80 0.06 0.04 0.02 0.14 0.12 0.06 0.04 0.02 0.14 0.12 -0.02 -0.04 -0.02 -0.04 6 5 1 ) [GeV] 4.5 0.8 zenith rec E 4 0.6 e-like cos( μ-like 3.5 0.4 3 0.2 0 2.5 2 -0.2 1.5 -0.4 1 -0.6 0.5 e-like -0.8 parameter (described in the text) for single-ring parameter (described in the text) for single-ring B A -1 0 0 0

0.1 0.1

80 60 40 20

0.08 0.08 -40 -60 -80 -20

0.14 0.12 0.06 0.04 0.02 0.14 0.12 0.06 0.04 0.02

B parameter Asymmetry

-0.02 -0.04 [deg] -0.02 -0.04 A A Asymmetry parameter parameter Asymmetry Asymmetry parameter parameter Asymmetry The The Figure 5: in the SK-I to SK-IV data (points) and MC (boxes). Figure 4: in the SK-I to SK-IV data (points) and MC (boxes). Measurements of the Atmospheric Neutrino Flux at Super-Kamiokande PoS(ICRC2015)1044 . 4600 4600 0.01] 0.01] × × -1 -1 (1998) (2006) 4400 4400 81 Phys. Rev. D73 Euan Richard . -like down-going e-like down-going µ 4200 4200 4000 4000 Climax NM parameter [count hr Climax NM parameter [count hr . Phys.Rev. . Phys. Rev. Lett. 3800 3800 . 3600 3600 1002.3471 3400 3400 1 1 0 2 0 2

0.8 0.8 1.8 1.8 0.6 0.4 0.2 1.6 1.4 1.2 0.6 0.4 0.2 1.6 1.4 1.2

Neutrino events [count day [count events Neutrino ] day [count events Neutrino ]

-1 -1 7 (2010) 092004. 4600 4600 0.01] 0.01] D81 × × -1 -1 4400 4400 . -like up-going µ e-like up-going Phys.Rev. 4200 4200 . 4000 4000 Climax NM parameter [count hr Climax NM parameter [count hr Detection of muons produced by cosmic ray neutrinos deep underground Evidence for High-Energy Cosmic-Ray Neutrino Interactions Atmospheric neutrino oscillation analysis with sub-leading effects in Super- Solar neutrino measurements in super-Kamiokande-I Evidence for Oscillation of Atmospheric Neutrinos 3800 3800 (1965) 196. 18 3600 3600 hep-ex/0508053 (1965) 429. 15 Events from four SK neutrino data samples, simultaneously fit against the predicted form of a 3400 3400 Phys. Lett. Lett. 1562. Kamiokande I, II, and III 112001. 1 1 0 0 2 2

0.8 1.8 0.8 1.8 1.2 0.6 0.4 0.2 1.6 1.4 1.4 1.2 0.6 0.4 0.2 1.6

Neutrino events [count day [count events Neutrino ] Neutrino events [count day [count events Neutrino ]

-1 -1 [1] C. V. Achar et al. [2] F. Reines, et al. [3] Y. Fukuda et al. [4] R. Wendell et al. [5] J. Hosaka et al. References mine the astrophysical neutrino spectra.measurements In could general, also further provide improvements feedback to tounderstanding the of the atmospheric the flux flux atmospheric simulations, neutrino and flux further as a both better a systematic background and a signal source. Figure 6: solar activity correlation accordingbased to on the the HKKM neutron count model,predicted at form where various of "Climax monitor the NM function stations differs around parameter" depending the is on Earth. the a data Although parameter sample. hard to see by eye, the Measurements of the Atmospheric Neutrino Flux at Super-Kamiokande PoS(ICRC2015)1044 . . . . Z. 110 . D74 (2004) D70 Euan Richard . Phys.Rev.Lett. Phys.Rev. 1403.1532 . . (2003) 418. . Phys. Rev. Lett. from Muon Neutrino . Astroparticle Physics . . Phys. Rev. A501 23 . . . θ . . 1502.05199 . 0902.0675 1004.2357 (2014) (18) 181801. (2015). 1010.3980 1112.6353 nucl-ex/0502021 Flux in IceCube e 112 ν 1104.5187 Nucl.Instrum.Meth. PTEP . . . . (2011) 123001. 1204.0626 . (2010) 48. D83 34 8 (2009) 102005. (2011) 012001. (2012) 131801. (2005) 055502. Phys.Rev.Lett. D79 . . (2011) 082001. 0801.4589 1103.0340 1311.4750 D83 108 . C72 Phys. Rev. (2012) 191802. . D84 108 Phys.Rev. Astropart.Phys. . . Phys. Rev. Phys.Rev. . . 1203.1669 Phys.Rev. Electron energy spectra, fluxes, and day-night asymmetries of B-8 solar The FLUKA atmospheric neutrino flux calculation Phys.Rev.Lett. (2008) 221803. (2011) 181801. (2014) 061802. . Measurement of the neutrino mass splitting and flavor mixing by MINOS Determination of the Atmospheric Neutrino Flux and Searches for New . Measurement of the Atmospheric Improvement of low energy atmospheric neutrino flux calculation using the The Super-Kamiokande detector Measurement of the atmospheric neutrino energy spectrum from 100 GeV to hep-ex/0606032 The Energy Spectrum of Atmospheric Neutrinos between 2 and 200 TeV with Observation of Electron Neutrino Appearance in a Muon Neutrino Beam A Search for a Diffuse Flux of Astrophysical Muon Neutrinos with the IceCube Observation of Reactor Electron Antineutrino Disappearance in the RENO 100 106 112 Physics Potential of a Long Baseline Neutrino Oscillation Experiment Using Measurement of Neutrino Oscillation by the K2K Experiment Precision Measurement of Neutrino Oscillation Parameters with KamLAND Three-dimensional calculation of atmospheric neutrinos Indication for the disappearance of reactor electron antineutrinos in the Double Phys.Rev.Lett. Precise Measurement of the Neutrino Mixing Parameter Observation of electron-antineutrino disappearance at Daya Bay Determination of the atmospheric neutrino spectra with the Frejus detector . (1995) 417. C66 (2012) 171803. (2003) (2) 269 . ISSN 0927-6505. neutrinos from measurements with NaCl dissolved inNeutrino the Observatory heavy-water detector at the Sudbury Phys.Rev.Lett. 108 Chooz experiment (2006) 072003. Experiment Phys.Rev.Lett. Disappearance in an Off-Axis Beam Phys.Rev.Lett. J-PARC Neutrino Beam and Hyper-Kamiokande JAM nuclear interaction model 19 023006. Phys. Physics with AMANDA-II the AMANDA-II Detector 400 TeV with IceCube (2013) 151105. 40-String Detector [6] B. Aharmim et al. [7] S. Abe et al. [8] F. An et al. [9] J. Ahn et al. Measurements of the Atmospheric Neutrino Flux at Super-Kamiokande [10] Y. Abe et al. [11] M. Ahn et al. [12] P. Adamson et al. [14] K. Abe et al. [13] K. Abe et al. [15] K. Abe et al. [16] M. Honda, et al. [17] G. Battistoni, et al. [18] G. Barr, et al. [19] K. Daum. [20] R. Abbasi et al. [24] R. Abbasi et al. [21] R. Abbasi et al. [22] R. Abbasi et al. [23] M. Aartsen et al. [25] Y. Fukuda et al.